1. Field of the Invention
The present invention relates to a road surface layer reproducing machine, and more particularly to one provided with multi-axle type rotors for scarifying and mixing asphalt pavement surface layers, the rotors of which are arranged in a direction perpendicular to a travelling direction of a vehicle body of such a machine and kept at certain temperatures.
2. Description of the Prior Art
Hitherto, road surface layer reproducing machines are well known as a machine for repairing the surface layer of an asphalt pavement body. In the operation, such a machine follows a road heating machine provided with a heating unit for heating the asphalt pavement body, and comprises, in a lower portion of its self-propelled vehicle body, rotors for scarifying and mixing a road paved with asphalt having been heated, the rotors of which are followed by screw spreaders and screeds.
The conditions where such conventional road surface layer reproducing machines can be employed are that the damages exist only in the surface layers of the asphalt pavement. The thickness of the surface layers to which such conventional machines can generally repair is said to be 3 to 5 cm (See the outlines of the asphalt pavement, Japan Road Association.).
At the time of repairing operations of such a conventional road surface layer repairing machine, a heating unit is separated from a scarifying/mixing unit. Therefore pavement surfaces once heated are cooled down by the time the scarifying/mixing unit reaches the heated portions of the pavement. In addition, because such a scarifying/mixing unit is not provided with a heating/heat-insulating means and has to conduct a mixing operation in an atmosphere at outdoor temperatures, the temperatures of the asphalt will drop rapidly.
The temperatures where the asphalt pavement can be scarified must be above the softening point of the asphalt contained in the pavement. It is requested that the average temperatures of the whole asphalt mixtures scarified should stay within a predetermined range at the time of rolling. According to the above-mentioned outlines of the asphalt pavement, such average temperatures are in a range of 110.degree. to 140 .degree. C.
If the depths of the pavement to which a scarifying operation is performed are below the softening point in temperature, the aggregates contained in the asphalt mixture are apt to be broken so that the surfaces of the aggregates to which no asphalt is coated are exposed. As a result the compaction effect of the asphalt mixture is impaired to a large extent.
In view of the requirements that the depths of the pavement to be scarified should be above the softening point in temperature and that the average temperatures of the whole scarified asphalt mixtures should be within the predetermined range immediately before start of rolling, conventional machines which are not provided with heating/heat-insulating means can scarify the pavement only to half the depths of the entire surface layers to be scarified. Consequently it is very difficult to reproduce the pavement which has been impaired to the entire depths of the pavement.
The mixing units of conventional road surface layer reproducing machines are provided with a one-axle type rotor which makes it difficult to conduct a uniform mixing operation of the asphalt mixtures. Particularly, in case such a mixing and heat-insulating operation is conducted with addition of various reproducing additives and fresh asphalt mixture by such conventional machines, there is an inclination to lack uniformity in the mixtures. Some conventional machines are equipped with a two-axle rotor which is arranged in parallel with the advancing direction of the vehicle to eliminate the lack of uniformity in the mixtures. But these machines lack a heating and heat-insulating means for the scarified surfaces which are exposed to atmosphere temperatures, resulting in a drop of the temperatures of the scarified surfaces. No such machines can improve the quality of the reproduced asphalt mixtures.